Once-through vapor generating and superheating unit



Nov. 21, 1961 E. A. PIRSH Filed May 27, 1955 ONCE-THROUGH VAPOR GENERATING AND SUPERHEATING UNIT PRESSURE /BREAK-DOWN STATION 18 m 42 TURBINE ATTEMPERATOR a se REDUCING 50 VALVE 20 I NUMBER 1 v 58 FLASH TANK 54 33 DEAERATOR DRTY NUMBER 2 CONDENSATE WATER 4 FLASH TANK TANK K 5 82 80 I 70 MAIN FEED COOLER v v 66 Pump A a 9 Cgogo 34 I 4 4 DEMINERALIZER 84 I 68 Low PREssuRE HEATER INVENTOR. EDWARD A. PIRSH J BY United States Patent Filed May 27, 1955, Ser. No. 511,496

8 Claims. (Cl. 60-105) The present invention relates in general to a oncethrough type vapor generating and superheating unit. More particularly, the invention relates to apparatus for use during starting-up and shutting-down periods. of a once-through type vapor generating unit.

In the operation of once-through type vapor generating units, it has heretofore been known that the tubes of the unit must be maintained at controlled low temperatures during the period of starting-up and shutting-down when the working fluid is not being delivered to the prime mover. During such periods, the tubes in the unit receive heat either by direct firing or by radiation from the hot slag and/or refractory within the unit and it is necessary that the working fluid circulation be maintained during such periods. Under these circumstances, the fluid which exits from the vapor generating unit is at a temperature greater than can be safely handled in the prime mover vapor condenser. Further, the fluid as it goes through the vapor generating unit is maintained at its normal working pressure. The combination of the high pressure and temperature of the fluid during the starting-up and shuttingdown periods has required special handling. In some cases, the fluid has been thrown away during these periods. Such a system is extremely expensive because the high quality liquids cost per pound is very high. However, in some cases Where the starting-up and shutting-down procedure is done only infrequently, the loss may be economically sustained.

Alternately, it has been suggested that the high pressure and temperature fluid exiting from the vapor generating unit bypass the turbine and enter a special condenser designed and fabricated to operate under these special conditions. Such a condenser is expensive because it must'be constructed for temperatures and pressures higher than that of the main condenser and with a capacity of approximately one third that of the main condenser.

The present invention contemplates a system for handling the fluid during starting-up and shutting-down periods in which the system is considerably simplified and less expensive than has been heretofore known. The present system includes a valve controlled conduit for conducting the exiting fluid from the vapor generating unit, a pressure reducing device in the conduit arranged to adiabatically reduce the pressure or" the em'ting fluid to a pressure whose saturated temperature is within the design operating limit of the prime mover condenser, flash tank means arranged to receive and separate the vapor from the liquid of the reduced pressure fluid, means for conducting vapor from the flash tank to either or both the prime mover condenser and/or a deaerating feed Water heater, and liquid conduits inter-connecting the flash tank to the vapor generator condensate system. The improved system may be further enhanced by providing a contact type heat exchanger or attemperator positioned downstream from the pressure reducing device and is arranged to cool the fluid to maintain a saturated temperature entering the flash tank.

Additionally, the system may include a tank for storing the dirty separated liquid from the flash tank and a liquid demineralizer which are so arranged that the liquid may be channeled through either or both before the liquid is returned to the prime mover condensate system.

In a more specific sense, the pertinent system mayv 3,009,325 Patented Nov. 21, 1961 include two flash tanks to be used with the first tank arranged to receive the fluid from the attemperator or the reducing device and with the first tank delivering the saturated vapor to a deaerator operating at a pressure whose saturated temperature is above but approaching the design temperature limit of the main condenser. The saturated liquid from the flash tank then enters a second tank where it is reduced in pressure to that of the main condenser With the separated steam going to the main condenser and the liquid to the condensate system.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating ad vantages and specific objects attained by its use, reference should be had to the accompanying drawing and descriptive matter in which there is illustrated and described a preferred embodiment of the invention.

In the drawing, there is illustrated a once-through type vapor generating and superheating unit 2 having an inlet header 4- in which a vaporizable fluid is introduced. The fluid thence flows in succession through wall tubes of a combustion chamber 6 and other parts of the unit to an intermediary header 8 at which point it has received sufficient energy to be completely vaporized. At this point, the vapor flows through a primary superheater 10, through a cross connection 12 and thence through a secondary superheater 14 from which it is delivered via line 15 and throttle valve 16 to a prime mover or turbine 18. Normally, the exiting vapor from the low pressure end of the turbine passes by the line 20 to a main condenser 22 where it is condensed at a low pressure. The condensed liquid then leaves the main condenser and flows through a condensate system back to the inlet header 4 of the vapor generating unit 2. The main condensate system consisting of a condensate pump 24, condensate discharge line 28, low pressure feed liquid heater 30, a deaerating feed liquid heater 3?. and a main feed pump 34 which delivers the fluid to the vapor generating unit 2.

In the operation of the vapor generating and super-.

heating unit, it becomes necessary to start-up and shutdown the power system and during which time, it is necessary to remove the turbine from the system while maintaining fluid circulation through the vapor generating and superheating unit due to heating therein. Accordingly, the present invention provides a valve controlled'independent fluid line 36 which takes exiting fluid from the vapor generating unit and bypasses the turbine 18, the valve 16 being closed. Also, there is provided an independent valve controlled line 38 which removes fluid from the vapor generating unit at the superheater crossover 12 so that during the shutdown period, the high temperature superheater '14 will not be cooled too rapidly. In each of the lines 36 and 38, there is a pressure breakdown or reducing station or device 40 which reduces the operating fluid pressure from its normal value to a much lower pressure by an adiabatic or throttling expansion process, the lower pressure having a saturated temperature which approximates the manufacturer's designed maximum operating temperature of the main condenser '22. A contact heat exchanger or attemperator 42 is positioned downstream from the pressure reducing device and is arranged to spray or admix cooled condensate from the condensate system by the line 44 and which is controlled by a temperature regulator 46 to always maintain the reduced pressure fluid at saturation temperature. Thus, the pressure reducing device and the attemperator combine to produce a saturated fluid under any startingup or shutting-down condition with such fluid being all- -vapor or a vapor-liquid mixture and which is at a temperature suflicient to allow it to be safely cooled in the prime mover main condenser 22 when expanded to the condensers pressure.

A fluid handling system receives the saturated reduced pressure fluid from the attemperator 42 and delivers it to the main condensate system line 28. This fluid handling system comprises a #1 flash tank 48 which is arranged to take the saturated fluid and separate the vapor from the liquid, and which in the present case, operates at approximately 150 p.s.i.a. The separated vapor then passes over a scrubber element 50 to remove all the moisture and into a delivery line 52 which is arranged to pass the saturated vapor through to the main condenser line 20 or the deaerator 32. A liquid temperature controlled valve 33, stop valves 54 are used to control this operation and a reducing valve 56 in the line reduces the vapor pressure from 150 p.s.i. to the operating pressure of the condenser which is normally about I-Ig. A water level controller 58 having a pressure reducing valve 58A, controls the rate of saturated liquid flow from the #1 tank 48 in response to liquid level changes therein and flashes the fluid to a pressure corresponding to that in the main condenser or approximately 5" Hg. The #2 flash tank 60 is arranged to receive the flashed fluid and separates the vapor and liquid with the vapor passing over scrubber element 62 into line '64 whence it is delivered to the main condenser 22. The liquid from the tank 60 is removed by a pump 66 and may be either delivered to the main condenser hot well by line 68 or to a further treatment system. A water level controller 70 regulates the quantity of liquid flow from the tank 60.

The fluid handling system is further arranged with a dirty water storage tank 72, the condensate storage tank 74, a cooler 76 in series with a demineralizer 78 and inter-connecting conduits 80, 82, 84 and 86 so that the liquid upon leaving the #2 flash tank 69 may be delivered to the condensate line 28 directly, through the demineralizer and/ or through the dirty water storage tank and/ or condensate tank.

The operation of the system and its advantages may be more readily understood by way of an explanation of the vapor generating and superheating starting-up procedure. When it is desired to start, condensate from the tank 74 or from the main condenser 22 is pumped through the condensate line 28 into the deaerator 32. The main feed pump 34 then circulates fluid through the vapor generating and superheating unit 2, into the outlet line 15. The turbine throttle 16 in line 18 is closed and the pressure is maintained at a normal operating value by the reducing station 40. The fluid is bypassed around the turbine in the valve controlled line 36 where its pressure is reduced to 150 psi. by the pressure breakdown device 40 and thence through the contact heat exchanger 42 into the #1 flash tank 48 and thence into #2 flash tank as previously described and on into the dirty water storage tank 72. When suflicient circulation is obtained in the vapor generating unit, fires are lit in the combustion chamber 6 and the outlet temperature of. the fluid is allowed to rise over a specified time period so as not to temperature shock the pressure parts of the system. As this temperature rises above 359 F., the fluid upon leaving the pressure reducing device 40 will be a mixture of vapor and liquid, but it Will be at a pressure low enough so that it may be cooled directly in the main condenser without damage thereto. The vapor and liquid are separated in the flash tank #1 with the vapor being routed to the deaerator 32 so as to conserve heat within the cycle. The liquid then passes to #2 flash tank and is reduced in pressure by the valve 58A to a pressure substantially that of the main condenser 22, as there is no valve in the line 64. The liquid is passed through the liquid handling system so that it may be either retained in the water storage tank 72 or cleaned by the demineralizer 78 or returned to the system. The steam passes to the condenser and is condensed in the normal manner.

The shutting-down system is similar to that described above, but the operations are in the reverse order.

The operation of the attemperator or direct heat exchanger is such that it will maintain the temperature to the fluid leaving the attemperater at the saturation temperature of the fluid, thus assuring that no fluid may go to the main condenser with a temperature greater than the maximum design value.

The present system provides apparatus which is inherently simple and inexpensive to reduce the temperature of the exiting fluid from the vapor generating and superheating unit with a minimum of cooling and in which arrangement, the main condenser is used to reject all heat from the cycle. This is accomplished by adiabatically reducing the pressure of the exiting fluid to a value which has a saturated temperature less than the maximum operating temperature of the main condenser, thus, the fluid may be cooled by the main condenser. In the present arrangement, there is provided a system whereby the reduced pressure fluid is separated into vapor and liquid components, each of which is handled independently so as to assure the most efiicient cooling. For instance, the vapor is normally utilized to heat the feed water in the deaerator while the liquid is returned to the condensate system.

Further, there is provided in the present system means for cleaning and storing the condensate so as to avoid introducing any contaminated liquid in the condensate system.

Another important advantage of the present system is that any impurities picked up by the condensate as it traverses the vapor generating unit and condensate system are concentrated by the adiabatic throttling process in the remaining liquid. Thus, this concentrated liquid can be handled more effectively for cleaning purposes.

The present invention is directed to once-through vapor generating and superheating units which operate either above or below the critical pressure of the vaporizable fluid. The pressure reducing device being designed to perform the adiabatic expansion according to the operating pressure of the vapor generator.

While in accordance with the provisions of the statutes, I have illustrated and described herein, a specific form of the invention now known to me, those skilled in the art will understand that changes may be made in the form of the apparatus discussed Without departing from the spirit of the invention covered by my claims, and that certain features of the invention may be used to advantage Without the corresponding use of other features.

What is claimed is:

1. In combination, a once-through vapor generating and superheating unit, a valve-controlled vapor conduit from the outlet of said unit conducting the superheated vapor during normal operation to a prime mover, a condenser arranged to receive vapor from said prime mover, a condensate system supplying condensed liquid to said vapor generating and superheating unit from said condenser, an independent valve controlled conduit conducting the exiting fluid from said vapor generating and superheating unit during starting-up and shuttingdown periods to a fluid handling system, said fluid handling system comprising pressure reducing means arranged to adiabatically reduce the pressure of said exiting fluid to a pressure Whose saturated temperature is within the designed operating limit of said condenser, flash tank means arranged to receive the reduced pressure fluid and to separate the vapor from the liquid, vapor conduits connecting said flash tank means to said condenser, and liquid conduit means inter-connecting said flash tank to said condensate system.

2. In combination, a once-through vapor generating and superheating unit, a valve-controlled vapor conduit from the outlet of said unit conducting the superheated vapor during normal operation to a prime mover, a condenser arranged to receive vapor from said prime mover,

a condensate system supplying condensed liquid to said vapor generating and superheating unit from said condenser, an independent valve controlled conduit conducting the exiting fluid from said vapor generating and superheating unit during starting-up and shutting-down periods to a fluid handling system, said fluid handling system comprising pressure reducing means arranged to adiabatically reduce the pressure of said exiting fluid to a pressure Whose saturated temperature is within the designed operating limit of said condenser, a contact heat exchanger arranged to admix cool liquid with said reduced pressure fluid, means controlling the supply of said cool liquid in response to the saturated temperature of the reduced pressure fluid, flash tank-means arranged to receive the reduced pressure fluid and to separate the vapor from the liquid, vapor conduits connecting said flash tank means to said condenser, and liquid conduit means interconnecting said flash tank to said condensate system.

3. In combination, a once-through vapor generating and superheating unit, a valve-controlled vapor conduit from the outlet of said unit conducting the superheated vapor during normal operation to a prime mover, a condenser arranged to receive vapor from said prime mover, a condensate system supplying condensed liquid to said vapor generating and superheating unit from said condenser including a vapor heated liquid deaerating means, an independent valve controlled conduit conducting the exiting fluid from said vapor generating and superheating unit during starting-up and shutting-down periods to a fluid handling system, said fluid handling system comprising pressure reducing means arranged to adiabatically reduce the pressure of said exiting fluid to a pressure Whose saturated temperature is within the designed operating limit of said condenser, flash tank means arranged to receive the reduced pressure fluid and to separate the vapor from the liquid, vapor conduits connecting said flash tank means to said condenser and deaerating means, valve means in said vapor conduits for selectively opening said tank to said condenser and/ or deaerating means, and liquid conduit means inter-connecting said flash tank means to said condensatesystem.

4. In combination, a once-through vapor generating and superheating unit, a valve-controlled vapor conduit from the outlet of said unit conducting the superheated vapor during normal operation to a prime mover, a condenser arranged to receive vapor from said prime mover, a condensate system supplying condensed liquid to said vapor generating and superheating unit from said condenser including a vapor heated liquid deaerating means, an independent valve controlled conduit conducting the exiting fluid from said vapor generating and superheating unit during starting-up and shutting-down periods to a fluid handling system, said fluid handling system comprising pressure reducing means arranged to adiabatically reduce the pressure of said exiting fluid to a pressure whose saturated temperature is within the designed operating limit of said condenser, flash tank means arranged to receive the reduced pressure fluid and to separate the vapor from the liquid, a liquid demineralizer, a dirty liquid storage tank, vapor conduits connecting said flash tank means to said condenser and deaerating means, valve means in said vapor conduits for selectively opening said tank means to said condenser and/or deaerating means, liquid conduit means inter-connecting said flash tank to said condensate system and to said dirty liquid storage and demineralizer, and valve means in said conduit means for selectively opening said flash tank to said condensate system via said dirty liquid tank and/or demineralizer.

5. In combination, a once-through vapor generating and superheating unit, a valve controlled vapor conduit from the outlet of said unit conducting the superheated vapor during normal operation to a prime mover, a condenser arranged to receive vapor from said prime mover, a condensate system supplying condensed liquid to said vapor generating and superheating unit from said condenser, an independent valve controlled conduit conducting the exiting fluid from said vapor generating and superheating unit during starting-up and shutting-down periods to a fluid handling system, said fluid handling system comprising a pressure reducing device in said conduit ar-, ranged to adiabatically reduce the pressure of said exiting fluid to a pressure whose saturated temperature approximates the designed operating limit of said condenser, a flash tank arranged to receive the reduced pressure fluid and to separate the vapor from the liquid, vapor conduits connecting said first named flash tank to said condenser, a second flash tank arranged to receive the separated liquid from said first named flash tank and to separate the liquid from the vapor, means reducing the pressure of the liquid passing from said first named flash tank to a value approximately that of said condenser, liquid conduit means inter-connecting said second flash tank to said condensate system, and vapor conduits connecting said second flash tank to said condenser.

6. in combination, a once-through vapor generating and superheating unit, a valve-controlled vapor conduit from the outlet of said unit conducting the superheated vapor during normal operation to a prime mover, a condensate system supplying condensed liquid to said vapor generating and superheating unit from said condenser including a vapor heated liquid deaerating means, an inde pendent valve controlled conduit conducting the exiting fluid from said vapor generating and superheating unit during starting-up and shutting-down periods to a fluid handling system, said fluid handling system comprising a pressure reducing device in said conduit arranged to adiabatically reduce the pressure of said exiting fluid to a pressure Whose saturated temperature is above, but approaching the designed operating limit of said condenser, 21 flash tank arranged to receive the reduced pressure fluid and to separate the vapor from the liquid, a liquid demineral-izer, a dirty liquid storage tank, vapor conduits connecting said first named flash tank to said condenser and deae-rating means, valve means in said vapor conduits for selectively opening said tank to said condenser and/ or deaerator, a second flash tank arranged to receive the separated liquid from said first named flash tank and to separate the liquid from the vapor, means for reducing the pressure of the liquid passing from said first named flash tank to a value approximately that of said condenser, liquid conduit means inter-connecting said second flash tank to said condensate system and to said dirty liquid storage and demineralizer, vapor conduits connecting said second flash tank to said condenser, and valve means in said liquid conduit means for selectively opening said flash tank to said condensate system via said dirty liquid tank and/or demineralizer.

7. In combination, a vapor generating and superheating unit, a valve-controlled vapor conduit from the outlet of said unit conducting the superheated vapor during normal operation to a prime mover, a condenser arranged to receive vapor from said prime mover, a condensate system supplying condensed liquid to said vapor generating and superheating unit from said condenser, an independent valve-controlled conduit conducting the exiting fluid from said vapor generating and superheating unit during starting-up and shutting-down periods to a fluid handling system, said fluid handling system comprising pressure reducing means arranged to adiabatically reduce the pressure of said exiting fluid to a pressure whose saturated temperature is in a range whose upper limit approximates the designed operating limit of said condenser, flash tank means arranged to receive the reduced pressure fluid and to separate the vapor from the liquid, vapor conduit means connecting said flash tank means to said condenser, and liquid conduit means interconnecting said flash tank means to said condensate system.

8. In combination, a vapor generating and super-heating unit, a valve-controlled vapor conduit from the outlet of said unit conducting a superheated vapor during normal operation to a prime mover, a condenser arranged to receive vapor from said prime mover, a condensate system supplying condensed liquid to said vapor generating and superheating unit from said condenser, an independent 5 valve-controlled conduit conducting the exiting fluid from said vapor generating and superheating unit during starting-up and shutting-down periods to a fluid handling system, said fluid handling system comprising pressure reducing means arranged to adiabatically reduce the pressure 10 reducing means, said pressure reducing means, flash tank 1 means and 'attemperator cooperating to reduce the pressure and temperature of said fluid to the extent that the saturation temperature corresponding to the pressure of the reduced pressure fluid is within the designed operating limits of said condenser, vapor conduit means connecting said flash tank means to said condenser, and liquid conduit means interconnecting said flash tank means to said condensate system.

References Cited in the file of this patent UNITED STATES PATENTS 1,728,375 Stender Sept. 17, 1929 1,934,667 Harter Nov. 7, 1933 2,747,373 Eggenberger et al May 29, 1956 2,844,004 Vogler July 22, 1958 

